there is actualy an entire set of clubs you can get for only 99 credits.
http://www.wgt.com/proshop/product.aspx?i=5c7bead8-8703-4af5-994c-5252740dc9a5&c=Bundles
they're an improvement for sure if you've been using starter or beginner clubs.
and just what has worked for me having to work with so few credits myself...but..
the other putters you could get just aren't worth it. stick with the beginner putter till you can get one of the higher end putters. worth more to be able to relatively easily ding it than how bad they can spray on the long putts if you miss just a little. the few rounds i played with a tour starter putter...it was absolutely not worth keeping. what looks like an improved club did not translate well on the courses at all..
then upgrade your 3w as soon as you can. a good 3w can make up a lot more yardage than a good driver. especialy when the par 3's start getting just out of reach. just from what i'd seen, the next driver up only gives you maybe 5 yards ( talking about going as cheap as you can) but, for very little you can upgrade your 3w by 20-30 yards for a very small amount. actualy even replacing your driver, as long as you're not worried about your stats because a 3w or any other club off the tee doesn't count as a fairway hit. anyways..
and then before long you'll have some more credits and that's when you're going to need to get you some wedges..and probably a driver...but that'll all come later.